The present invention relates to thermoplastic molding compositions with improved mechanical properties comprising at least four different components.
The molding compositions comprise one or more styrene copolymers, one or more polyamides, at least one graft rubber, and also at least one terpolymer whose content of oligomers is low.
The molding compositions can, if appropriate, comprise, as additional components, for example, further rubbers, an at least monofunctional anhydride whose molar mass is smaller than 3000 g/mol, and, if appropriate, fibrous or particulate fillers or a mixture of these, and also, if appropriate, further additives.
The present invention further relates to preparation of these thermoplastic molding compositions, and also to the use of the molding compositions for production of moldings, for example for household items, for electronic components, for household equipment, for garden equipment, for medical-technology equipment, and for motor vehicle components.
Various polymer blends composed of styrene copolymers and of polyamides have been known for many years, for example from EP-A 202 214, EP-A 402 528, EP-A 784 080, and DE-A 100 24 935.
EP-A 202 214 discloses thermoplastic compositions to the person skilled in the art which comprise not only a graft polymer component (for example an ABS resin) but also a polyamide component (such as nylon) and a terpolymer (for example composed of the monomers styrene, acrylonitrile, and maleic anhydride).
EP-A 402 528 discloses an impact-resistant thermoplastic mixture which comprises not only a graft polymer (such as ABS) but also a polyamide resin, a terpolymer (for example composed of styrene, of a dicarboxylic anhydride and of maleimide), and also, if appropriate, a further polymer component.
Document EP-A 784 080 describes polymer compositions which comprise at least three components, where component A is a graft polymer, component B is a thermoplastic polyamide, and component C is a terpolymer composed of, for example, styrene, acrylonitrile, and maleic anhydride. The compositions described in EP-A 784 080 can also comprise, as further component, phthalic anhydride.
DE-A 100 24 935 describes polymer blends which have at least four components. The compositions described comprise at least one elastomeric graft polymer component, at least one polyamide, at least one compatibilizer having polar groups, and also at least one vinyl copolymer.
While some of the thermoplastic compositions described in the prior art have high heat resistance, good tensile strain at break, and increased weathering resistance, there is often a high degree of anisotropy in relation to impact resistance of the moldings produced therefrom.
Anisotropy is generally the directional dependency of a physical property. For use in production of moldings that can withstand mechanical load, it is very important that the moldings produced do not have a high degree of impact-resistance anisotropy, since there is generally more than one direction in which mechanical loads can arise.
Binary blends composed of polyamides and of styrene copolymers have very poor toughness, because of the incompatibility between polyamide and SAN (matrix and styrene-acrylonitrile copolymer). It has been previously disclosed that the use of functionalized SAN polymers can significantly increase the toughness of polyamide/styrene copolymer mixtures. Furthermore, these products have interesting properties such as high impact resistance and good flowability and chemicals resistance.
Studies on the “in-situ” compatibilization of the components in styrene copolymer/polyamide mixtures have been disclosed in the literature to the person skilled in the art, for example in the following publications: V. J. Triacca, S. Ziaee, J. W. Barlow, H. Kesskula, D. R. Paul, Polymer 32, 1401 (1991); B. Majundar, H. Keskkula, D. R. Paul, N. G. Harvey, Polymer 35, 4263 (1994); C. W. Lee, S. H. Ryu, H. S. Kim, J. Appl. Polym. Sci., 64, 1595 (1997); R. A. Kudva, H. Kesskula, D. R. Paul, Polymer 39, 2447 (1998); C. Lacasse, B. D. Favis, Adv. Polym. Techn. 18, 255 (1999); R. A. Kudva, H. Kesskula, D. R. Paul, Polymer 41, 239 (2000).
Suitable compatibilizers acting between polyamides and styrene copolymers are especially styrene-acrylonitrile-maleic anhydride terpolymers, styrene-N-phenylmaleimide-maleic anhydride terpolymers, and polymers with methyl methacrylate-maleic anhydride content (see, for example, EP-A 0 946 644).
The amino or carboxy end groups of the polyamides generally react with the functional groups of the co- and terpolymers mentioned, the result being in-situ production of copolymers which provide the improved compatibility between the styrene copolymer phase and the polyamide phase. These polymer mixtures with modified interface are generally termed polymer alloys, as, for example, described by L. A. Utracki, “Polymer Alloys and Blends”, Hanser Publishers, Munich Vienna N.Y., 1989.
The styrene copolymer/polyamide PA 6 molding compositions known hitherto are like other polymer blends in having high anisotropy of impact resistance. If, for example, a series of experiments uses test specimens obtained from large components parallel to and, respectively, perpendicularly to the direction of flow, there are sometimes large differences in relation to impact resistance. This mechanical anisotropy can lead to considerable disadvantages in the use of the moldings, e.g. cracks or fractures in the molding.